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Dynamic deuteron polarization in irradiated D-Ammonia (ND3 and its first use in a high energy photon beam

1984; Elsevier BV; Volume: 227; Issue: 1 Linguagem: Inglês

10.1016/0168-9002(84)90098-6

1872-9576

W. Meyer, K.H. Althoff, W. Havenith, O. Kaul, H. Riechert, E. Schilling, G. Sternal, Walter Thiel,

Atomic and Subatomic Physics Research

Abstract We have dynamically polarized the deutorons in deuterated ammonia (ND3) at 1 K, 0.5 K and at about 200 mK in a magnetic field of 2.5 T. The paramagnetic radicals were created by irradiating the material under liquid argon at 90 K (‘high temperature’ irradiation) with electrons from the 20 MeV injection linac of the Bonn synchrotron. Electron paramagnetic resonance (EPR) measurements identified the radicals as ṄD2. First target asymmetry measurements of the reaction γd ↑ → pn with ND3 as target material in a dilution refrigerator were performed at the Bonn 2.5 GeV electron synchrotron. Starting with a deuteron polarization of 31% (using‘ high temperature’ irradiated material) the polarization went up to 44% after additional irradiation at about 200 mK with the photon beam. This polarization value corresponds to an overall polarization of 13.2% of all nucleons in ND3. The increase of the polarization could be observed up to a dose of 8 × 1014 equivalent quanta/cm2. The subsequent resistance of the polarization to radiation damage is more than one order of magnitude higher than that of butanol. These results mean a considerable improvement with respect to the deuterated alcohol materials which are currently used in high energy physics experiments with polarized deuteron targets. The dependence on the microwave frequency of the polarizations of deuterons and unsubstituted protons was examined at 1 K in order to gain insight into the prevailing mechanism of dynamic nuclear polarization (DNP). These measurements disagree with the equal spin temperature (EST)-hypothesis. They rather give evidence for a more complex behaviour apparently involving more than one polarization mechanism. It is attempted to explain these observations at 1 K with a differential solid state model. Furthermore, we present a series of DNP-signals as measured with our deuteron magnetic resonance (DMR)-system at various microwave frequencies. An unusual change of the DMR-signal shape was observed.